1. Field of the Invention
This invention generally relates to electronic array circuitry and, more particularly, to a sensor array able to monitor multiple environmental features with a single electrical measurement.
2. Description of the Related Art
Early detection of pressure ulcers is extremely important in order to avoid the onset of potentially life-threatening and costly problems. Pressure ulcers are caused by pressure against the skin (typically in areas of bone protrusions), which leads to localized ischemia and, ultimately, tissue necrosis. In 2007, there were 5.2 million cases of pressure ulcers worldwide; 2.4 million cases (60,000 resulting in death) in the US alone. According to a recent study (5,000 hospitals from 2003 to 2005), pressure ulcers have one of the highest occurrence rates, along with failure to rescue and postoperative respiratory failure. Pressure ulcer etiology is mostly associated with the following three factors: (a) pressure, (b) temperature, and (c) moisture.
Sustained pressure, leading to reduced blood flow in the skin or deep muscle tissue, is considered the prevalent factor. A commonly used pressure level of 35 millimeters of mercury (mmHg) is considered a danger threshold, which can be as high as 200 mmHg over a bony prominence1. Also, friction, leading to skin tissue damage, and shear are implicated. Regarding temperature, in healthy individuals, a local increase of skin temperature results in increased blood flow. In risk patients, blood flow is not adequate to reduce temperature. A skin temperature increase by 1.2° C. over 24/48 hours increases the risk of forming a pressure ulcer. Finally, increased moisture levels (e.g. perspiration, incontinence) makes the skin more susceptible to damage, as increased skin pH expedites cell deterioration2.
This problem is currently addressed by electronic devices that measure specific metrics on the surface of the body. The majority of devices (proposed or currently in the market) involve detecting high pressure points. This is achieved by obtaining two-dimensional pressure maps of part of, or of the entire area of the body in contact with the surface upon which it rests (seat, bed mattress, etc.). Representative commercially available systems of this type are the Wellsense MAP® system3 (a Class I exempt device, costing about $4,000 per year and comprising of “thousands” or sensor points), and the XSensor flexible capacitive pad system4 (Costing $9,500-$12,000 per sheet, with 1,664 sensor points).
Other options include (a) measuring the impedance of the human skin as a function of frequency (spectroscopic impedance), in order to detect the onset of sub-epidermal tissue necrosis5, and (b) the capacitive measurement of the sub-epidermal skin layers to detect changes in sub-epidermal moisture (SEM), a biophysical marker of damaged tissue6.
It would be advantageous if a low-cost device existed that made the monitoring and detections of pressure-related environmental factors more practical.    1 R. Thomas, Does pressure cause pressure ulcers?, Journal of the American Medical Directors Association, 11(6), 395-405, 2010    2 P. Slachta, Assessing risk of pressure- and moisture-related problems in long-term care patients, Wound Care Advisor, 2(3), 8-11, May/June 2013    3 http://www.healthleadersmedia.com/page-4/TEC-291902/Technology-Tackles-the-Pressure-Ulcer    4 http://www.xsensor.com/Foresite    5 http://www.bruinbiometrics.com/images/Brocures/SEMScannerDeviceBrochure-Distributors_RevB.pdf    6 http://news.berkeley.edu/2015/03/17/smart-bandages-detect-bedsores/